1. Field of the Invention
The invention relates generally to a remote meter reading system in which data derived from a meter is interrogated by and transmitted to a remote station, such as a mobile unit, and is further processed.
2. Description of the Prior Art
Considerable efforts have been made in recent years to increase the efficiency of reading consumption meters of the type that are standard equipment of and usually furnished by utility companies. Basically, the manual system has remained unaltered ever since these meters first came into common use. Previous efforts to eliminate or substantially reduce the high labor input for reading meters have been devoted to systems in which the meters are interrogated from a remote station with signals being transmitted via utility power lines, telephone lines or radio transmitters. Each such system, however, has serious disadvantages, raises unresolved technical complexities or is cost prohibitive. One such effort relates to transmitting the information via existing power transmission lines. The "line" system precludes, however, direct communication between the interrogating station and the meter inasmuch as the signals cannot be simply passed through the transformers scattered throughout the path of the transmission lines. In order to overcome signal interference by transformers, various signal by-passes, as well as through-passes, have been suggested.
Included in such approaches have been hybrid systems as exemplified by U.S. Pat. No. 3,656,112, in which a wireless link is employed to transmit the signals from one side of the transformer to the other side. It would appear, however, that no practical and/or commercially satisfactory solution has as yet been found. As noted in U.S. Pat. No. 3,900,842, the transmission by-pass approach, or radio transmission of signals from and to a control station, results in systems that are not only complex and cost prohibitive but even more importantly, are not dependable. The last mentioned patent proposed to overcome these difficulties by modifying the signals before and after they are transmitted through the transformer.
Other technical considerations and disadvantages germane to the use of power line data transmission includes the need to filter out or eliminate interferences from high amplitude noises generated by common electric gear and equipment.
While the use of radio frequencies (RF) as a transmitting medium would appear, at first glance, to have considerable merit, it has been found, upon more detailed consideration, that present systems are not acceptable for widespread applications for a variety of reasons. The RF transmission is basically omnidirectional and in order to enhance its directional characteristics large scale antennas and inordinately expensive microwave equipment has to be employed. But even the use of such equipment does not, however, completely eliminate or sufficiently diminish the difficulty of accurately pointing such devices in the direction of the meter location.
While heavy expenditures can be reduced by the use of lower frequencies, but still in the RF range, such use, however, will require coded interrogation and encounter interference from high voltage power lines, adverse weather conditions and radiation from numerous other sources. The unregulated and regulated band of RF is presently saturated with commercial and private users which constitute additional sources of interferences.
The use of telephone lines for transmission of data, as suggested for instance in U.S. Pat. No. 3,609,727, also raises numerous technical as well as non-technical obstacles. It is immediately apparent that such a system requires not only the existence of a telephone proximate to the meter to be monitored, but also the availability and/or cooperation of the telephone user when the monitoring is to take place. The resulting tone pulses transmitted over telephone wires are subject to interferences from cross-talk, power line radiation, simultaneous line traffic, variable line attenuation and similar conventional occurrences, which may alter or destroy the meter data. Aside from this aspect, on which opinions vary, phone tariff considerations have impeded or restrained the acceptance of the system.
Many of the prior art systems require for proper meter monitoring a significant modification or replacement of present day meters. It is estimated that several hundred million utility consumption meters are installed in this country. Hence any system that will require substantial alteration of the meter will have significant economic ramifications which may defeat or detrimentally affect the acceptance of the system. A typical approach for modifying a meter for use in a remote meter reading system is shown in U.S. Pat. No. 3,566,384.